Process for measuring the value of carbon content of a steel bath in an oxygen top-blowing converter



July 4, 1967 PROCESS FOR MEASURING THE VALUE OF CARBON CONTENT OF ASTEEL Decurburizing Value of curbo n conrenf -velocii'y -of the steelboth Deccrburizing occelerurion (in kg/min) (in kg/min/sec) TAKAYOSHIOHTA ETAL 3,329,495

BATH IN AN OXYGEN TOP-BLOWING CONVERTER Filed Sept. 22, 1964 2Sheets-Shed 1 I 1 2 f '3 (in minures) FIG. I (c) a E 1A: in 1 n 1 "flIr-Time (in minufes) lNVENTORS Tokcyoshi Ohio Tomohiko Aku'ku MinoruNishiwoki Hideo Yoshizumi dad/W July 4, 1967 TAKAYOSHI OHTA ETAL PROCESSFOR MEASURING THE VALUE OF CARBON CONTENT OF A STEEL BATH IN AN OXYGENTOP-BLOWING CONVERTER Filed Sept. 22, 1964 2 Sheets-Sheet 2 Waste gas FG 2 from converter Waste gas CO analyz r CO2 ono'yzer flow meter (colli002" Fi I Recording I Recording Addition Carbon content of the steelbath Division Value of carbon content of the steel bath LTapping controlstep I liar change points Multiplication @ecarburizing velocity I Toftalcarbon content 7 o the c arged raw material iron ZCO IRecordingI l I l lIntegration Defferentiation l l I Amount of decar- Decarburizingbul'iZOtiOnACi acceleration Subtraction -I l 1 Recording l ConvertingWeight of the mechflnism molten steel Detection of pecu- Predeterminedstandard value of carbon content INVENTORS Takayoshi Ohta Tomohiko AkutaMinoru Nishiwaki Hideo Yoshizumi United States Patent PROCESS FORMEASURING THE VALUE OF CAR- BUN CONTENT OF A STEEL BATH IN AN OXY- GENTOP-BLOWING CONVERTER Takayoshi Ohta, Hikari, and Tomohiko Akuta, MinoruNishiwaki, and Hideo Yoshizumi, Kitakyusliu, Japan, assignors to YawataIron & Steel Co., Ltd., and Yokoyama Engineering Co., Ltd., Tokyo,Japan, both Japanese corporations Filed Sept. 22, 1964, Ser. No. 398,337Claims priority, application Japan, Sept. 26, 1963, 38/ 51,394 2 Claims.(Cl. 75-60) This invention relates to a process for measuring the valueof carbon content of a steel bath in an oxygen top-blowing converterduring the blowing operation.

In the operation of an oxygen top-blowing converter it is important tomake the value of carbon content of the steel bath at the time oftapping steel therefrom coincide with the predetermined target value.However, in the conventional operating method the value of carboncontent of the steel bath was estimated on the basis of the perceptionand experience of operators by their eye-measurements of flame andspark, because taking out the samples continuously from the steel bathfor analysis during the blowing operation is almost impossible.Therefore, it was very diflicult to constantly hit the target value ofcarbon content of the steel bath at the time of tapping.

The inventors have discovered a method of simply and precisely measuringthe value of carbon content of a steel bath in an oxygen top-blowingconverter.

That is, by detecting the amount of flow of waste gas issued from theconverter and the amounts of carbon monoxide and carbon dioxidecontained in said waste gas, the scientific control of the tapping timeof steel from the converter is made possible.

An object of the present invention is to provide a method of making thevalue of the carbon content of a steel bath in an oxygen top-blowingconverter at the time of tapping steel therefrom coincide with apredetermined target value of the steel bath by measuring the value ofcarbon content which, in turn, is accomplished by detecting the amountof flow of waste gas issued from the converter and the amounts of carbonmonoxide and carbon dioxide contained in said waste gas.

Another object of the present invention is to provide a method ofprecisely measuring the value of carbon content of a steel bath in theconverter by detecting the amount of flow of waste gas issued from theconverter and the amounts of carbon monoxide and carbon dioxidecontained in said waste gas and further compensating for the amount ofdecarburization of the steel bath at the time when a peculiar changeoccurs in the decarburizing velocity.

Other objects of the present invention will be made clear by thefollowing explanation and the accompanying drawings.

FIGURE 1a is a diagram showing the relation between the value of carboncontent of a steel bath and the time.

FIGURE 1b is a diagram showing the relation between the decarburizingvelocity and the time.

FIGURE 1c is a diagram showing the relation between the decarburizingacceleration and the time.

FIGURE 2 is a system diagram of the present invention.

One of the practical applications of the present invention is asfollows: From a waste gas issued from an oxygen top-blowing converter,the decarburizing velocity is detected by measuring the amount of flowof said waste gas issued from the converter and the compositions of saidwaste gas, then by integrating the thus detected decarburizing velocity,the amount of decarburization of a ice steel bath at a certain timeafter ignition may be calculated. Since the total amount of carboncontent of the material charged in the converter may be calculated, thevalue of carbon content of the steel bath may be easily calculated bysubtracting said amount of decarburization of the steel bath from thetotal amount of carbon content of the material. However, as errors inmeasurements are liable to occur in the above mentioned process, it isnecessary to correct such errors by detecting the moment when sharpchanges in the decarburization velocity curve occur by measuring thedecarburizing acceleration calculated from the decarburizing velocityand to compensate for the amount of the decarburization, which compriseserrors, by a correct one which corresponds to the standard value ofcarbon content of the steel bath at that detected moment. In this way avery precise value of carbon content of a steel bath may be calculated.

In the operation of a converter, the carbon contained in the charged rawmaterial will be oxidized by oxygen blowing, whereby carbon monoxide andcarbon dioxide will be produced according to the following chemicalreactions:

By the above reaction formulae, from one molecular weight (kg.) ofcarbon (12 kg.) there is produced one molecular weight (kg) of carbonmonoxide or carbon dioxide, having a volume of 22.4 m. in the standardstate, respectively. Therefore, on the basis of the above relations itis possible to calculate the amounts of carbon monoxide or carbondioxide contained in waste gas issued from the oxygen top-blowingconverter. Practically, if the flow rate of the waste gas produced by 0blowing is measured, whereby, for instance, its value at t, minutesafter the ignition is expressed as F (Nm. /hour), and the compositionsof said waste gas obtained at the same moment are analyticallydetermined, the decarburizing velocity at t, minutes after the ignitionwill be represented by the formula:

in which (CO), (percent) and (CO (percent) designate the concentrationsof carbon monoxide and carbon dioxide obtained by analyzing the wastegas caught at t, minutes after the ignition.

Therefore, the amount of decarburization for t, minutes after theignition, AC (kg), may be calculated, for instance, by continuouslyintegrating the value given by the Formula 1 by means of an electronicintegrating circuit or by carrying out an addition ofthe value ofmicrotime by means of an electronic computer. For convenience ofexplanation, however, AC will be here calculated by integrating thevalue of each minute, as shown by the following formula:

Further, the total amount of carbon, 2C (kg), contained in the chargedsteel-manufacturing material, which comprises, for instance, pig ironand scrap, may be .shown by the following formula:

ZC -AC'i 1001 (W +W,,) (percent) wherein 1; is the yield of manufacturedsteel.

Thus, by measuring the value of carbon content of the steel bath at anymoment during the blowing operation according to the Formula 4, theblowing operation may be automatically controlled. That is, the blowingoperation may be stopped just immediately before the calculated value ofcarbon content will coincide with the predetermined target valuethereof, whereby the end point of blowing may be scientifically andautomatically found in combination with a computing control device.

The method of the present invention shall be explained more in detailwith reference to the drawings. FIGURE 11: shows an example of thechange in the value of canbon content of the steel bath with theprogress of blowing. FIGURE 11) shows an example of the change in thedecarburizing velocity, and FIGURE an example of the change in thedecarburizing acceleration. The amount of decarburization AC (kg) at t,minutes after the ignition, as determined by the Formula 2, isrepresented by the area of the hatched part in FIGURE 1b. If the amountof AC, (kg) is to be expressed in the term of carbon content (percent)of the steel bath, it will be represented by the length of the segment AA, in FIGURE 1a. The segment HA; obtained by subtracting the segment A Afrom the segment m1, in FIGURE 1a represents the C (percent) of theFormula 4.

An embodiment of the method according to the present invention shall beexplained with reference to FIGURE 2. At first, the calculations ofaddition and multiplication shown by the double enclosures in FIGURE 2are carried out in order to determine the decarburizing velocity J 2 dtby the Formula 1 by using, for instance, an electronic computer or anelectronic computing circuit, while inputing thereto the analysis valuesof the concentrations of carbon monoxide and carbon dioxide (CO), and(CO obtained by an analyzer respectively, and the amount of flow rate Fof the waste gas continuously measured by a gas flow meter. Then, byintegrating this decarburizing velocity, the amount of decarburizationAC is determined. When the value of AC, is subtracted from the totalamount of carbon 2C of the charged raw material iron as calculated inadvance, and the thus obtained residue is divided by the amount ofmolten steel (W +W as calculated in advance, while taking the yield ofsteel into consideration, the value of carbon content of the steel bathmay be automatically calculated at any time during the blowingoperation.

According to experiments made by the inventors, however, it is foundthat, though the value of carbon content of the steel bath may bemeasured by the above mentioned method, many errors in measurements areapt to occur as, (a) the error ratio in measurement of carbon content inpig iron is usually at least 2%, resulting in more than *-0.06% error ofcarbon content value in the steel bath in the initial state, (b) evenslight errors in the measurements of the waste gas by the flow meter andgas analyzer are apt to be gradually accumulated so as to produce largeerrors in the integrating calculation, (c) the carbon dioxide containedin the waste gas is apt to dissolve in cooling water which is used inadjusting the temperature of the waste gas, and ((1) gas leakage betweenthe converter mouth and hood causes error in measuring waste gas fiowrate. Therefore, the total error in measuring decarburization AC by theabove mentioned method becomes more than il0%, which is proved by theinventors experiments. This results in rendering the above mentionedmethod valueless in the actual operation, particularly for low carbonsteel blowing in which the carbon content is less than 0.10% and theallowance of the value of carbon content of the steel bath requires sucha high precision as less than :t0.0l% error, and therefore, a furtherprocess should be used for this purpose, as explained in the following.

In FIGURE 10, the ratio of change in the decarburizing velocity at eachmoment, that is, the decarburizing acceleration calculated from thedecarburizing velocity, is represented. t t and t represent the timeafter ignition, at which the value of the decarburizing accelerationshows a change in the direction of its signal or a value greater thatthe predetermined one. The values of the decarburizing velocitycorresponding to the times t t and t in FIGURE 1b show the abruptchanges. According to runs made by the inventors it was discovered that,in general, the decarburizing velocity and decarburizing acceleration atany time are closely correlated with the carbon content of the steelbath at the corresponding time. As shown in FIGURE 1a, the value of thecarbon content of the steel bath at the above mentioned times 1 t and tcorrespond to C (percent), C (percent) and C (percent), respectively,and these values show originally the specific inherent values accordingto the type of the converter, the blowing conditions and the kind ofsteel.

Therefore, according to the method of the present invention thedecarburizing velocity is continuously measured during the blowingoperation according to Formula 1 as above mentioned and then thedecarburizing acceleration, that is, the ratio of change in thedecarburizing velocity at each moment, is also continuously calculatedfrom the decarburizing velocity, by means of, for instance, anelectronic computor or an electronic circuit, whereby the times at whichpeculiar points in the curves of the decarburizing velocity anddecarburizing acceleration appear, that is, t t t in FIGURE 11) orFIGURE 1c may be detected. If such points are detected, the exact valueof the carbon content of the steel bath at the corresponding time may beobtained on the basis of the relation shown in FIGURE 1a which ispredetermined according to the type of the converter, the blowingconditions and the kinds of the steel.

This process step will be explained more in detail with reference toFIGURE 2. The decarburizing velocity calculated by Formula 1 iscontinuously differentiated by means of, for instance, an electroniccomputor or an electronic computing circuit to obtain the decarburizingacceleration, d c/dl If such a peculiar change occurs, in which thecalculated value of the decarburizing acceleration exceeds a certainpredetermined value or shows a change in the direction of its signal, anelectric control signal is automatically issued from an electric controldevice at that time.

On the other hand, the predetermined standard value of carbon content ofthe steel bat-h [C] percent corresponding to the time, at which theabove mentioned peculiar change is detected, is put into a covertingmechanism. In this converting mechanism, the total carbon weight 230 ofthe charged material iron and weight of the molten steel have alreadybeen memorized. And the calculation is carried out by the followingformula to determine the correct amount of decarburization AC ECB-[C]percent weight of molten steel =AC (5) The amount of decarburization ACwhich includes errors obtained by integrating the Formula 2 arecancelled and replaced by the correct amount of decar-burization ACgiven by the Formula 5.

Thus, the value of carbon content incorrectly measured, is compensatedto the correct one of carbon content set by an electric control deviceor an electronic computor. The subsequent integrating calculation may becontinued by using this value as an initial value. Thus, by detectingthe time of change in the decarburizing velocity by means of thedecarburizing acceleration obtained by differentiating the decarburizingvelocity and inputting the standard value of carbon content of the steelbath at that time, at which such a change is detected, into a convertingmechanism, it is possible to amend such errors as the analyzing error ofthe carbon content in raw material, accumulated error by the integratingcalculation and gas analysing error by dissolution of carbon dioxide.

Thus, a very precise value of carbon content of the steel bath may bemeasured by repeating this procedure several times during the process ofthe blowing operation.

It is also possible to amend the errors by detecting the times ofchanges t t and t by means of the decarburizing velocity as shown inFIGURE 1b and putting into the converting mechanism the standard Valueof carbon content corresponding to such detected time.

Although the above mentioned explanation of this invention is related tothe continuous precise measuring process of carbon content of steelbat-h during the blowing operation, combining the amending method ofcarbon content of steel at peculiar change points of the decarburizingreaction to continuous calculation of car-bon content of steel byintegration, it is obviously possible to apply the detecting method ofcarbon of steel at separate peculiar change points independently.

What We claim is:

1. A process for tapping steel from an oxygen top-blowing converter,said steel having a predetermined carbon content, which comprisesmeasuring the amount of waste gas issued from said converter, measuringthe amount of carbon monoxide and carbon dioxide contained in said wastegas, calculating the decarburization velocity from the amount of wastegas and the amount of carbon monoxide and carbon dioxide in said wastegas in accordance with the following formula wherein is thedecarburizing velocity, F is the amount of waste gas, (CO) is the amountof carbon monoxide in said waste gas, and (CO is the amount of carbondioxide in said waste gas; differentiating the said decarburizationvelocity thereby obtaining the decarburizing acceleration, noting anychanges in the value of said decarburizing acceleration, calculating thecarbon content of the steel at the time of said changes, and tapping thesteel at the exact time the carbon centent of the steel reaches apredetermined value.

2. A process for tapping steel from an oxygen topblowing converter, saidsteel having a predetermined carbon content, which comprises (a)measuring the amount of waste gas issued from said converter and theamounts of carbon monoxide and carbon dioxide contained in said wastegas,

(b) calculating the decarburization velocity from the amount of Waste.gas and the amount of carbon monoxide and carbon dioxide in said wastegas in accordance with the formula set forth in claim 1,

(c) differentiating the decarburization velocity to thereby obtain thedecarburizing acceleration,

(d) noting the times at which peculiar change points appear in thedecarburizing acceleration,

(e) calculating the carbon content of the steel at the time of saidchanges,

(f) calculating the correct amount of decarburization in accordance withthe following formula 2C [C] percent X weight of molten steel=ACfwherein EC is the total carbon weight of the charged material iron and[C] percent is predetermined standard value of carbon content of thesteel bath corresponding to the time the above-mentioned peculiar changeis detected,

(g) calculating the amount of decarburization was AG,

by integrating the decarburizing velocity,

(h) amending the AG, by the said correct amount of decarburization ACand (i) tapping the steel at the exact time the carbon content of thesteel reaches a pre-determined value.

References Cited UNITED STATES PATENTS 2,595,792 5/1952 Jordan -603,218,842 "ll/1965 Ludwig et al. 73-23 RICHARD C. QU-EISSER, PrimaryExaminer.

J. FISHER, C. I. MCCLELLAND,

Assistant Examiners.

1. A PROCESS FOR TAPPING STEEL FROM AN OXYGEN TOP-BLOWING CONVERTER,SAID STEEL HAVING A PREDETERMINED CARBON CONTENT, WHICH COMPRISESMEASURING THE AMOUNT OF WASTE GAS ISSUED FROM SAID CONVERTER, MEASURINGTHE AMOUNT OF CARBON MONOXIDE AND CARBON DIOXIDE CONTAINED IN SAID WASTEGAS, CALCULATING THE DECARBURIZATION VELOCITY FROM THE AMOUNT OF WASTEGAS AND THE AMOUNT OF CARBON MONOXIDE AND CARBON DIOXIDE IN SAID WASTEGAS IN ACCORDANCE WITH THE FOLLOWING FORMULA -(DC/DT) =FI(((CO)+(CO2))/100) WHEREIN -(DC/DT) IS THE DECARBURIZING VELOCITY, F1IS THE AMOUNT OF WASTE GAS, (CO) IS THE AMOUNT OF CARBON MONOXIDE INSAID